The disclosure of Japanese Patent Application No. 2001-120571 filed on Apr. 19, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention generally relates to a brake control system and method for braking a vehicle. More particularly, the invention relates to a brake control system that controls a braking force applied to each wheel based on an operational force applied to a braking member such as a brake pedal, and an amount of displacement of the braking member.
2. Description of Related Art
A brake control system in a vehicle such as an automobile, which controls the braking force of each wheel based on the force applied to a braking member and the amount of displacement of the braking member is well known. For example, a brake control system disclosed in Japanese Patent Application Laid-Open Publication No. 2000-247219 is such that a pressure sensor detects a master cylinder pressure Pm and a stroke sensor detects a depression stroke Sp of the brake pedal. The brake control system then calculates a target deceleration Gpt based on the master cylinder pressure Pm and calculates a target deceleration Gst based on the depression stroke Sp. The brake control system then calculates a final target deceleration Gt based on the target decelerations Gpt and Gst and controls the braking force of each wheel in accordance with this final target deceleration Gt.
In particular, the brake control system disclosed in the aforementioned publication is configured such that if any sensor changes from a normal state to an abnormal state, a deviation xcex94Gt between the calculated final target deceleration Gt which includes the detection results of the sensor in which there is an abnormality and the calculated final target deceleration Gt which excludes the detection results of the sensor in which there is an abnormality is calculated. The final target deceleration Gt is then corrected with the deviation xcex94Gt such that the deviation xcex94Gt is gradually reduced.
Therefore, according to the brake control system proposed above, even if a sensor changes from a normal state to an abnormal state, there will not be a sudden change in the final target deceleration Gt. As a result, it is possible to reliably prevent a sudden change in the braking force and resultant deterioration of stability and controllability of the vehicle, and therefore a sense of discomfort to the vehicle operator, and the like.
Generally, in a brake control system the following calculations are performed: calculation of the target deceleration Gpt based on the master cylinder pressure Pm, calculation of the target deceleration Gst based on the depression stroke Sp, and calculation of the final target deceleration Gt based on the target decelerations Gpt and Gst. Then the brake control system controls the braking force of each wheel in accordance with this final target deceleration Gt. The target decelerations Gpt and Gst are calculated with respectively different patterns for the same amount of braking force applied by the vehicle operator.
For example, in a region where the braking amount by the vehicle operator is small, the depression stroke Sp reflects the amount of braking required by the vehicle operator more accurately than the master cylinder pressure Pm. Conversely, in a region where the braking amount by the vehicle operator is large, the master cylinder pressure Pm reflects the amount of braking required by the vehicle operator more accurately than the depression stroke Sp. Therefore, the target deceleration Gst is calculated in the region where the braking amount is small and the target deceleration Gst is set to contribute greatly to the final target deceleration Gt in the region where the braking amount is small. Also, the target deceleration Gpt is calculated in the region where the braking amount is large and the target deceleration Gpt is set to contribute greatly to the final target deceleration Gt in the region where the braking amount is large.
According to the brake control system proposed above, in the event that there is an abnormality in the pressure sensor, the target deceleration Gst is set to the final target deceleration Gt. Conversely, in the event that there is an abnormality in the stroke sensor, the target deceleration Gpt is set to the final target deceleration Gt. As a result, when there is an abnormality in any sensor, the relationship between the final target deceleration Gt and the braking amount by the vehicle operator changes, thus giving the vehicle operator a sense of discomfort when braking.
It is an object of the invention to provide a method and a brake control system of a vehicle, which is configured so as to control the braking force of each wheel based on a force applied to a braking member, and an amount of displacement of the braking member. The main objective of this invention is to reduce a sense of discomfort felt by the vehicle operator during braking when the detected value of the force applied to the braking member or the detected value of the amount of displacement of the braking member is abnormal. This is achieved by reducing a degree of change in the relationship between the final target deceleration Gt and the amount of braking by the vehicle operator generated when the detected value of the force applied to the braking member or the detected value of the amount of displacement of the braking member is abnormal.
According to an aspect of the invention, a method for controlling braking of a vehicle includes detecting a force applied to a braking member of the vehicle by an operator, detecting a displacement amount of the braking member, and calculating a final target brake control amount. The final target brake control amount further includes calculating a first target brake control amount on the basis of a first value of the force applied, calculating a second target brake control amount on the basis of a second value of the displacement amount, and calculating the final target brake control amount on the basis of the first target brake control amount calculated and the second target brake control amount calculated. When one of the values detected is abnormal, and the other one of values detected is normal, a degree of contribution of one of the first target brake control amount and the second target brake control amount is decreased, which is calculated on the basis of the abnormal detection value, to the final target brake control amount. A mode for calculating the other one of the first target brake control amount and the second target brake control amount is changed, which is calculated on the basis of the normal detection value, so as to reduce an influence of the decrease of the degree of contribution on the final target brake control amount.
According to another aspect of the invention, a brake control system for a vehicle includes a first detector that detects a force applied to a braking member of the vehicle by an operator of the vehicle, a second detector that detects a displacement amount of the braking member of the vehicle upon application of the force to the braking member, and a controller that calculates a first target brake control amount on the basis of a first value detected by the first detector, a second target brake control amount on the basis of a second value detected by the second detector, a final target brake control amount on the basis of the first target brake control amount and the second target brake control amount. When one of the values detected by the first detector and the second detector is abnormal, and the other one of values detected by the first detector and the second detector is normal, the controller decreases a degree of contribution of one of the first target brake control amount and the second target brake control amount, which is calculated on the basis of the abnormal detection value, to the final target brake control amount. The controller also changes a mode for calculating the other one of the first target brake control amount and the second target brake control amount, which is calculated on the basis of the normal detection value, so as to reduce an influence of the decrease of the degree of contribution on the final target brake control amount.
In the foregoing aspect of the invention, in the event that one of the detected p value of the force and the detected value of the amount of displacement of the braking member is abnormal, the amount of contribution of the target brake control amount which is calculated based on the abnormal detected value to the final target brake control amount is decreased. Then the calculation mode of the target brake control amount which is calculated based on the other detected value, that is, the normal value, is changed so as to reduce the effect caused by the decrease on the final brake control amount. Therefore, the likelihood that inappropriate brake control will be performed as a result of the target brake control amount which is calculated based on the abnormal detected value is able to be reliably reduced. In addition, a change in the relationship between the braking force of each wheel and the braking amount by the vehicle operator which is generated when one of the detected value of the force and the detected value of the amount of displacement of the braking member is abnormal, is reliably reduced. This reduction in the degree of the change in relationship thus reliably reduces a sense of discomfort felt by the vehicle operator during braking when the detected value of the force applied to the braking member or the detected value of the amount of displacement of the braking member is abnormal.
According to another aspect of the invention, the controller changes the mode for calculating the other one of the first and the second target brake control amount calculated on the basis of the normal detection value such that the decrease in the degree of contribution of one of the first target brake control amount and the second target brake control amount has a reduced influence on a relationship between the force applied to the braking member of the vehicle by the operator of the vehicle and the final target brake control amount.
According to the aforementioned aspect of the invention, the calculation mode of the target brake control amount that is calculated based on the other detected value, that is, normal value, is changed by changing the relationship between the target brake control amount and the normal detection value. Therefore, a change in the relationship between the amount of the brake controlled by the operator and the final target deceleration, which is generated when one of the detected value of the force and the detected value of the amount of displacement of the braking member becomes abnormal, is reliably reduced. This makes it possible to reduce the change more reliably compared, for example, with when only the contribution amount of the target brake control amount based on the other detected value, that is, the normal value, to the final target brake control amount is changed.
According to another aspect of the invention, when the force applied to the braking member of the vehicle and the displacement amount of the braking member have normal values, the controller calculates the final target brake control amount as a weighted sum of the first target brake control amount and the second target brake control amount.
In the aforementioned aspect of the invention, the amount of contribution of the target brake control amount which is calculated based on the abnormal detection value to the final target brake control amount is decreased to 0. This reliably prevents the braking force of the respective wheels from being inappropriately controlled due to the final target brake control amount that is calculated based on the abnormal detected value.
According to another aspect of the invention, the controller changes the mode for calculating the other one of the first and the second target brake control amount calculated on the basis of the normal detection value such that the decrease in the degree of contribution of one of the first target brake control amount and the second target brake control amount has a reduced influence on a relationship between the force applied to the braking member of the vehicle by the operator of the vehicle and the final target brake control amount.
According to another aspect of the invention, when the force applied to the braking member of the vehicle by the operator of the vehicle detected by the first detector has an abnormal value, the controller changes the mode for calculating the second target brake control amount such that a ratio of the second target brake control amount to the final target brake control amount is increased to be larger than a ratio of the second target brake control amount to the final target brake control amount obtained when the force applied to the braking member has a normal value in an area where the force applied to the braking member of the vehicle by the operator is small.
According to another aspect of the invention, when the displacement amount of the braking member of the vehicle detected by the second detector has an abnormal value, the controller changes the mode for calculating the first target brake control amount such that a ratio of the first target brake control amount to the final target brake control amount is increased to be larger than a ratio of the first target brake control amount to the final target brake control amount obtained when the displacement amount of the braking member of the vehicle has a normal value in an area where the force applied to the braking member of the vehicle by the operator is large.
According to still another aspect of the invention, when the force applied to the braking member of the vehicle and the displacement amount of the braking member have normal values, the controller calculates the final target brake control amount as a weighted sum of the first target brake control amount and the second target brake control amount.
According to still yet another aspect of the invention, when the force applied to the braking member of the vehicle and the displacement amount of the braking member have normal values, the controller calculates the final target brake control amount to a weighted sum of the first and the second target brake control amounts. When one of the force applied to the braking member of the vehicle and the displacement amount of the braking member has an abnormal value and the other value has a normal value, the controller sets a weight to the one of the first and the second target brake control amounts calculated on the basis of the abnormal detection value to 0 so as to set the degree of contribution of the one of the first and the second target brake control amounts calculated on the basis of the abnormal detection value to the final target brake control amount to 0.